Spent nuclear fuel assemblies that are nuclear fuel assemblies used in nuclear power plants, for example, and extracted from nuclear reactors after being loaded and burned in the nuclear reactors are called recycled fuel assemblies. The recycled fuel assemblies contain highly radioactive substances such as fission products (FP). Accordingly, the recycled fuel assemblies are generally cooled in a cooling pit of a nuclear power plant, for example, for a certain period of time. The recycled fuel assemblies are then stored in a cask that is a recycled fuel assembly storage container having a radiation shielding function and used for transportation and storage, delivered to a reprocessing plant or an interim storage facility by a vehicle or a vessel, and stored therein until being reprocessed.
To store the recycled fuel assemblies in the cask, a recycled fuel assembly storage basket formed of a material having neutron absorbing power, and is a collection of storage spaces called cells in which recycled fuel assemblies are stored, is used. The recycled fuel assemblies are inserted into the storage spaces formed in the recycled fuel assembly storage basket, one by one. In this manner, the recycled fuel assemblies maintain appropriate intervals and are prevented from reaching criticality while being transported, and an appropriate holding force relative to vibrations during transportation, events that can be assumed, and the like is secured. Patent Documents 1 to 5 are, examples of such conventional recycled fuel assembly storage baskets. Patent Document 6 discloses a method for forming spaces in which recycled fuel assemblies are stored, by intersecting and combining plate-shaped members made of boron-aluminum (B—Al) material, with one another.    [Patent Document 1] Japanese Patent Application Laid-open No. 2004-020568    [Patent Document 2] Japanese Patent Application Laid-open No. 2004-069620    [Patent Document 3] Japanese Patent Application Laid-open No. 2004-163120    [Patent Document 4] Japanese Patent Application Laid-open No. 2005-208062    [Patent Document 5] Japanese Patent Application Laid-open No. H6-94892    [Patent Document 6] Japanese Patent Application Laid-open No. 2001-201595